Moon on his Warpstar (Flight Warpstar)
They were battle partners in the GSA.
After being ambushed by a group of strong Demon Beasts and their ship being badly damaged, they jumped through a wormhole as a last ditch effort to escape.
They ended up crash landing on the planet they currently live on. They didn't have enough materials to repair the ship or build a new one, so they ended up living there.
They also didn't manage to contact anyone in the GSA until after Nightmare's defeat, so they were assumed KIA for a long period of time.
While living together on the peaceful planet for years, they ended up developing feelings for eachother and became a couple.
They end up getting married some time after Nightmare's defeat, with all remaining Star Warriors, GSA members, friends and allies invited.
Moon's thoughts on Obsidian
"Obsidian can be very... energetic and cheerful when off-mission, but that's why I love him."
Obsidian's thoughts on Moon
"Moon can be really quiet, and maybe even a bit blunt sometimes, but I can't help love 'im regardless~ ♡"